diff options
Diffstat (limited to 'common')
| -rw-r--r-- | common/misc.js | 38 | ||||
| -rw-r--r-- | common/signing.js | 73 |
2 files changed, 74 insertions, 37 deletions
diff --git a/common/misc.js b/common/misc.js index 8894d60..d6b9662 100644 --- a/common/misc.js +++ b/common/misc.js @@ -8,9 +8,7 @@ /* * IMPORTS_START - * IMPORT sha256 * IMPORT browser - * IMPORT is_chrome * IMPORT TYPE_NAME * IMPORT TYPE_PREFIX * IMPORTS_END @@ -45,32 +43,6 @@ function gen_nonce(length) // Default 16 return Uint8toHex(randomData); } -function get_secure_salt() -{ - if (is_chrome) - return browser.runtime.getManifest().key.substring(0, 50); - else - return browser.runtime.getURL("dummy"); -} - -function extract_signed(signature, data, times) -{ - const now = new Date(); - times = times || [[now], [now, -1]]; - - const reductor = - (ok, time) => ok || signature === sign_data(data, ...time); - if (!times.reduce(reductor, false)) - return undefined; - - try { - return JSON.parse(decodeURIComponent(data)); - } catch (e) { - /* This should not be reached - it's our self-produced valid JSON. */ - console.log("Unexpected internal error - invalid JSON smuggled!", e); - } -} - /* csp rule that blocks all scripts except for those injected by us */ function csp_rule(nonce) { @@ -89,7 +61,7 @@ const report_only_header_name = "content-security-policy-report-only"; function is_csp_header_name(string, include_report_only) { - string = string && string.toLowerCase() || ""; + string = string && string.toLowerCase().trim() || ""; return (include_report_only && string === report_only_header_name) || csp_header_names.has(string); @@ -118,12 +90,6 @@ function is_privileged_url(url) return !!/^(chrome(-extension)?|moz-extension):\/\/|^about:/i.exec(url); } -/* Sign a given string for a given time */ -function sign_data(data, now, hours_offset) { - let time = Math.floor(now / 3600000) + (hours_offset || 0); - return sha256(get_secure_salt() + time + data); -} - /* Parse a CSP header */ function parse_csp(csp) { let directive, directive_array; @@ -193,8 +159,6 @@ const matchers = { /* * EXPORTS_START * EXPORT gen_nonce - * EXPORT extract_signed - * EXPORT sign_data * EXPORT csp_rule * EXPORT is_csp_header_name * EXPORT nice_name diff --git a/common/signing.js b/common/signing.js new file mode 100644 index 0000000..2171714 --- /dev/null +++ b/common/signing.js @@ -0,0 +1,73 @@ +/** + * part of Hachette + * Functions related to "signing" of data, refactored to a separate file. + * + * Copyright (C) 2021 Wojtek Kosior + * Redistribution terms are gathered in the `copyright' file. + */ + +/* + * IMPORTS_START + * IMPORT sha256 + * IMPORT browser + * IMPORT is_chrome + * IMPORTS_END + */ + +/* + * In order to make certain data synchronously accessible in certain contexts, + * hachette smuggles it in string form in places like cookies, URLs and headers. + * When using the smuggled data, we first need to make sure it isn't spoofed. + * For that, we use this pseudo-signing mechanism. + * + * Despite what name suggests, no assymetric cryptography is involved, as it + * would bring no additional benefits and would incur bigger performance + * overhead. Instead, we hash the string data together with some secret value + * that is supposed to be known only by this browser instance. Resulting hash + * sum plays the role of the signature. In the hash we also include current + * time. This way, even if signed data leaks (which shouldn't happen in the + * first place), an attacker won't be able to re-use it indefinitely. + * + * The secret shared between execution contexts has to be available + * synchronously. Under Mozilla, this is the extension's per-session id. Under + * Chromium, this is the key that resides in the manifest. + * + * An idea to (under Chromium) instead store the secret in a file fetched + * synchronously using XMLHttpRequest is being considered. + */ + +function get_secret() +{ + if (is_chrome) + return browser.runtime.getManifest().key.substring(0, 50); + else + return browser.runtime.getURL("dummy"); +} + +function extract_signed(signature, signed_data) +{ + const match = /^([1-9][0-9]{12}|0)_(.*)$/.exec(signed_data); + if (!match) + return {fail: "bad format"}; + + const result = {time: parseInt(match[1]), data: match[2]}; + if (sign_data(result.data, result.time)[0] !== signature) + result.fail = "bad signature"; + + return result; +} + +/* + * Sign a given string for a given time. Time should be either 0 or in the range + * 10^12 <= time < 10^13. + */ +function sign_data(data, time) { + return [sha256(get_secret() + time + data), `${time}_${data}`]; +} + +/* + * EXPORTS_START + * EXPORT extract_signed + * EXPORT sign_data + * EXPORTS_END + */ |